Angular position sensors

ABSTRACT

A rotatable insulating disc carries a closed grid of conductors over one part of one side and a similar but open grid over another part. An oscillator is coupled to a coil which is parallel to the disc and produces a cyclically varying but symmetrical field through the disc. Two pairs of pick-up coils sense, for respective orthogonal directions, the distortion of the field by the closed grid and detector circuits coupled to the pick-up coils provide signals representing the sine and cosine of the angular position of the disc which may carry a compass needle.

United States Patent 15] 3,699,558 Hendley et al. 51 Oct. 17, 1972 [54]ANGULAR POSITION SENSORS 2,936,623 5/1960 Quist ..340/l96 72 Inventors:D i Alfred Hendhy, London 3,217,308 1 1/1965 Maxwell ..340/1 96 gland;sipko I Boersma Delft, 3,594,741 7/1971 Ellison ..340/1 96 NetherlandsPrimary ExaminerThomas B. Habecker [73] Assignee: Decca Llmlted, London,England Attorney Mawhinney and Mawhinney [22] Filed: July 13, 1970 211Appl. No.: 54,224 [57] ABSTRACT A rotatable insulating disc carries aclosed grid of conductors over one part of one side and a similar but[30] Forelgn Application Pnorlty Data open grid over another part. Anoscillator is coupled y 14, 1969 Great Bl'ltam to a coil which isparallel to the disc and produces a cyclically varying but symmetricalfield through the [52] US. Cl ..340/196, 33/204 0,336/79 disc Two pairsof pick up coils sense f respective [51 hit. Cl. ..G08c 19/06 orthogonaldirections, the distortion of the field by the [58] Fleld of Search..33/204 Q; 340/196 closed g and detector circuits coupled to the p upcoils provide signals representing the sine and [56] References Citedcosine of the angular position of the disc which may UNITED STATESPATENTS carry a compass needle- 705,482 7/1902 Thiermann ..'....340/l9613 Claims, 1 Drawing Figure ANGULAR POSITION SENSORS FIELD OF THEINVENTION is particularly suitable for providing an indication of theangular position of a compass needle.

SUMMARY OF THE INVENTION According to the invention an angular positionsensor for a rotatable member comprises means for producing a cyclicallyvarying magnetic field that is spatially regularvthrough a plane ofrotation of the member, means on the member for distorting the field inaccord with the members angular position, means for sensing thedistortion of the field in two orthogonal directions parallel to thesaid plane and means for deriving electrical signals representative ofthe sensed distortion in a respective direction.

With this construction it is readily possible to obtain signals of whichone has maxima and minima corresponding to positions of the member inquadrature with the positions resulting in maxima and minima of theother signal. It is accordingly possible to obtain signals representingat least approximately the sine and cosine of the angular position ofthe member. The accuracy of this representation may be improved bycarefu-l design of the means for introducing the distortion: even so, insome circumstances a sufficiently accurate indication of the angularposition can be obtained merely by detecting (for example) the minima ofthe signals and their equality.

Conveniently each sensing means comprises a pair of pickup coilsspanning regions displaced in a respective one of two orthogonaldirections parallel to the said plane; the means for deriving electricalsignals may comprise means responsive to the difference between signalsinduced in the respective coils by the flux of the magnetic fieldtherethrough. Conveniently detector circuits are arranged to formsignals representing in magnitude and sense the sine and cosine of theangular position of the said member.

Conveniently each pair of coils span two abutting semicircular regions.The means for producing the magnetic field may comprise a transmittercoil disposed parallel to the said plane and an oscillator coupled tothe coil for producing alternating current flow in the coil. Aparticularly convenient and potentially robust construction is providedby arranging the member between the transmitter coil and the pickupcoils, the two pairs of pickup coils being arranged in spaced-apartparallel planes and embracing regions substantially coextensive with thearea of the transmitter coil.

As indicated hereinbefore the invention is particularly suitable for usewith magnetic compasses. The obtaining of an electrical indication ofthe position of a compass needle, especially for use in auto-pilots, hasbeen difficult to achieve with relatively simple devices. In aconstruction in accord with the present invention the compass needle maybe mounted for rotation with the aforementioned member. The magneticfield, owing to its regularity, will not affect the response of theneedle to a planetary magnetic field. Moreover, the frequency of thecyclic variation of the field may be relatively high, for example in theregion of l MIIL, for the same purpose.

The means on the member conveniently comprise a conductive screenextending in said plane over part of the said member. The screen maycomprise a closed grid of metallic conductors. It would be convenient toprovide a similar grid over an opposite part of the member in order toobtain pivotal balance of the member. However, the balancing grid wouldneed to comprise an open network in order not to distort the magneticfield as does the closed grid.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing illustratesone preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In this example, a push-pullsine-wave oscillator l of frequency in the region of 1 MHz. is coupledto a circular transmitter coil 2 formed as a printed circuit on thesurface of a thin insulating disc. For convenience of illustration thedisc itself is not shown. The number of turns in the coil is optionaland depends on the impedance necessary to match the output impedance ofthe oscillator 1. When energized by the oscillator l the coil 2 producesan axial field which at least near the coils axis is substantiallysymmetrical in a plane transverse the axis. Parallel to and spaced apartfrom the coil 2 is another insulating disc (not shown for convenience).Each side of this disc carries a pair of pickup coils (3, 4 and 5, 6respectively). Each pair of coils spans two abutting semicircularregions constituting a circular region coaxial with the area of the coil2 energized by the oscillator 1. The two pairs of coils are inquadrature: thus if the regions spanned by one pair 3, 4 are divided byan East-West line, the regions spanned by the other pair 5, 6 aredivided by a North-South line. The pickup coils are single turn coils;each pair share a conductor extending along the common or dividingdiameter of the respective two regions.

For each coil in the pair of coils 3 and 4 the primary winding 7 of arespective transformer 8 is coupled across a gap provided between theend of the respective diametral conductor 9 and the adjacent end of thesemicircular part of each coil. The secondary windings 11 of thetransformers 8 are each coupled to each of two detector circuits l4 and15. The circuit 14 includes oppositely poled diodes 16 and 17 and aseries pair of output resistors 18 and 19 in shunt with smoothingcapacitors 20, 21 respectively. The secondary windings 11 are coupledjointly by a conductor 10 to the junction of the capacitors 20 and 21.The terminal 12 is connected to the junction of the resistors 18 and 19.The circuit 14 forms at the terminal 12 a signal corresponding to thedifference between the maximum magnitude of the signal flowing in thecoil 3 for positive half-cycles and the maximum magnitude of the signalflowing in the coil 4 during negative half-cycles; The similar circuit15 forms a similar signal derived from the negative half-cycles of thesignal induced in the coil 3 and the positive half-cycles of the signalinduced in the coil 4. The signals induced in the coils 3 and 4 will bedifferent owing to distortion introduced in a manner to be described.

A circuit 14a corresponding to the circuit 14 is connected between acosine output 12a and the secondary windings of transformers 8aconnected to the coils 5 and 6 as the transformers 8 are connected tothe coils 3 and 4. A circuit a corresponding to the circuit 15 isconnected between the transformers 8a and the terminal 12. The outputsat the pairs (12, 13) and (12a, 13a) of the output terminals representin magnitude and sense the sine and cosine of the angular position ofadisc 22.

Mounted for rotation about the common axis of the coils, between thepickup coils and the transmitter coil, is the insulating disc 22 mountedon a pivot 23 for rotation with a compass needle 27. The disc 22 bears aprinted circuit on its upper surface, that is to say the surface nearerthe pickup coils. On one half of the upper surface of the printedcircuit is formed a conductive grid 24 in the form of a closed ring 25with parallel bars 26 extending across the ring 25. On the other half ofthe disc 22 there is provided a similar, but open grid 24a, the bars 26aof the grid being separated from part of the outer ring 25a so as not toconstitute a closed circu'it.

With this construction, the closed barred grid acts as a short-circuitedcoil and thereby as a screen; accordingly the magnetic field above itwill be considerably reduced in intensity compared with the fieldimmediately above the other part of the disc 22. This distortion of themagnetic field is picked up by the sensing coils to provide outputscorresponding to the angular position of the rotatable disc 22. Withcareful design of the screen the electrical outputs can representaccurately the sine and cosine of that angular position.

The coils and disc may be disposed inside a cylindrical containercontaining a suitable liquid.

The compass needle is preferably aligned with one of the axes ofsymmetry of the grids.

We claim:

1. An angular position sensor for a compass needle, said sensorcomprising a rotatable member mounted for rotation in accord with therotation of said needle and coaxially therewith, said member extendingin a plane normal to its axis of rotation, means for producing acyclically varying magnetic field that is spatially regular about theaxis of rotation of the said member, a conductive closed grid means ofparallel conductors disposed on the said member and extending over itnormal to said axis, whereby said field is distorted in accord with themembers angular position, respective means for sensing the distortion ofthe field in each of two orthogonal directions normal to said axis andcircuit means coupled to said means for sensing for deriving electricalsignals representative of the sensed distortion in each direction. I J

2. An angular position sensor as claimed in claim 1 in which the meansfor sensing each comprise two pick-up coils spanning regions displacedin a respective one of two orthogonal directions parallel to the saidplane and the means for deriving electrical signals comprise meansresponsive to the difference between signals induced in the respectivecoils by the flux of the magnetic field.

3. An angular position sensor as claimed in claim 2 in which dgtectorcircu'ts are coupled to the ickup coils for pro ucmg signasrepresentative of e sine an cosine of the angular position of themember.

4. An angular position sensor as claimed in claim 2 in which each pairof coils span two abutting semicircular regions.

5. An angular position sensor as claimed in claim 4 in which the meansfor producing the magnetic field comprises a coil disposed parallel tothe said plane and an electrical oscillator coupled to the coil.

6.An angular position sensor as claimed in claim 5 in which the memberis disposed between the transmitting coil and the two pairs of pickupcoils.

7. An angular position sensor as claimed in claim 6 in which the twopairs of pickup coils are arranged in spaced apart parallel planes andembrace regions substantially co-extensive with the area of thetransmitting coil.

8. An angular position sensor as claimed in claim 7 in which the meansfor distorting comprises a conductive screen extending in said planeover part of the said member.

9. An angular position sensor as claimed in claim 8 in which the screencomprises a closed grid of conductors.

10. An angular position sensor as claimed in claim 9 in which over apart of the member, opposite the part which carries the closed grid ofconductors, is an open grid of otherwise similar configuration to thatof the closed grid. i

11. An angular position sensor for a compass needle which is rotatableabout an axis, said sensor comprising an insulating disc mounted to movewith said needle for rotation about said axis; a closed circuit griddedscreen means of parallel conductors extending over part of said memberon a surface thereof normal to said axis; a first coil disposed in aplane parallel to said disc and spaced from said disc along said axis;and a pair of coils extending in a second plane parallel to the saiddisc and spaced along said axis therefrom on the side of said discremoter from said first coil, said coils of said pair of coils beingspaced apart in said second plane.

12. An angular position sensor as set forth in claim 11, furthercomprising a second pair of coils extending in a third plane parallel tosaid disc and spaced along said axis therefrom on the side thereofremoter from said first coil, said coils of said second pair of coilsbeing spaced apart in said third plane.

13. An angular position sensor as set forth in claim 12, furthercomprising signal generating means coupled to said first coil andrespective circuits each associated with one of said pairs of coils fordetermining differences in signals induced in the coils of therespective pair.

1. An angular position sensor for a compass needle, said sensorcomprising a rotatable member mounted for rotation in accord with therotation of said needle and coaxially therewith, said member extendingin a plane normal to its axis of rotation, means for producing acyclically varying magnetic field that is spatially regular about theaxis of rotation of the said member, a conductive closed grid means ofparallel conductors disposed on the said member and extending over itnormal to said axis, whereby said field is distorted in accord with themember''s angular position, respective means for sensing the distortionof the field in each of two orthogonal directions normal to said axisand circuit means coupled to said means for sensing for derivingelectrical signals representative of the sensed distortion in eachdirection.
 2. An angular position sensor as claimed in claim 1 in whichthe means for sensing each comprise two pick-up coils spanning regionsdisplaced in a respective one of two orthogonal directions parallel tothe said plane and the means for deriving electrical signals comprisemeans responsive to the difference between signals induced in therespective coils by the flux of the magnetic field.
 3. An angularposition sensor as claimed in claim 2 in which detector circuits arecoupled to the pick-up coils for producing signals representative of thesine and cosine of the angular position of the member.
 4. An angularposition sensor as claimed in claim 2 in which each pair of coils spantwo abutting semicircular regions.
 5. An angular position sensor asclaimed in claim 4 in which the means for producing the magnetic fieldcomprises a coil disposed parallel to the said plane and an electricaloscillator coupled to the coil.
 6. An angular position sensor as claimedin claim 5 in which the member is disposed between the transmitting coiland the two pairs of pickup coils.
 7. An angular position sensor asclaimed in claim 6 in which the two pairs of pickup coils are arrangedin spaced apart parallel planes and embrace regions substantiallyco-extensive with the area of the transmitting coil.
 8. An angularposition sensor as claimed in claim 7 in which the means for distortingcomprises a conductive screen extending in said plane over part of thesaid member.
 9. An angular position sensor as claimed in claim 8 inwhich thE screen comprises a closed grid of conductors.
 10. An angularposition sensor as claimed in claim 9 in which over a part of themember, opposite the part which carries the closed grid of conductors,is an open grid of otherwise similar configuration to that of the closedgrid.
 11. An angular position sensor for a compass needle which isrotatable about an axis, said sensor comprising an insulating discmounted to move with said needle for rotation about said axis; a closedcircuit gridded screen means of parallel conductors extending over partof said member on a surface thereof normal to said axis; a first coildisposed in a plane parallel to said disc and spaced from said discalong said axis; and a pair of coils extending in a second planeparallel to the said disc and spaced along said axis therefrom on theside of said disc remoter from said first coil, said coils of said pairof coils being spaced apart in said second plane.
 12. An angularposition sensor as set forth in claim 11, further comprising a secondpair of coils extending in a third plane parallel to said disc andspaced along said axis therefrom on the side thereof remoter from saidfirst coil, said coils of said second pair of coils being spaced apartin said third plane.
 13. An angular position sensor as set forth inclaim 12, further comprising signal generating means coupled to saidfirst coil and respective circuits each associated with one of saidpairs of coils for determining differences in signals induced in thecoils of the respective pair.